The intake of grass and rush (Juncus effusus L.) by goats grazing rush-infested grass pasture

The intakes of rush and grass by goats grazing rush-infested reseeded pasture (rush ground cover, 5.9%) were measured in three periods between July and September in one year, using n -alkanes as dietary markers. Diet composition and intakes were measured at intertussock sward heights maintained at 3–4 cm and 5–6 cm and at an intertussock sward height maintained at 3–4 cm where the rushes had previously been grazed by goats to reduce rush green stem height to 0.75 of that of ungrazed tussocks.
There was no effect of intertussock sward height or initial rush green stem height on the dietary proportion (overall mean 0.51) or dry matter (DM) intake of rush but there was an effect of period, which was related to changes in sward conditions over the experiment. Rush intake was positively related to the amount and accessibility of green rush stems and grass intake to intertussock sward height. Digestibility of DM of the diet, measured using n -alkanes, was high (overall mean 0.71), suggesting that the nutritive value of the rush is greater than previously estimated from in vitro digestibility measurements. Under these conditions, it appears that the goats select a mixed diet and the results are consistent with animals selecting food items to maximize their rate of nutrient intake.     

Herbage potassium levels in a permanent pasture under grazing

Herbage potassium levels were measured in 1986 in a permanent pasture under continuous grazing with cattle and receiving 200 kg N ha⁻¹. In April, before grazing started, K concentration in the herbage was relatively uniform across the pasture, with a value of 1·9 ± 0·038% K in the herbage dry matter. In July, a significantly lower concentration of herbage K was found in the grazed areas of the pasture (1·8 ± 0·10%) compared with the level (2·4 ± 0·088%) found in the rejected areas of the sward. The difference between the grazed and rejected areas was similar in September, with 1·6 ± 0·087% and 2·2 ± 0·172% K, respectively, in the herbage dry matter. This result suggests that herbage growth in the grazed areas might have been limited by K supply and highlights the need for more information on the K requirements of grazed grassland.     

Heavy grazing effects on stem elongation and internode allometry: Insights from a natural pasture grass

Limited plant stem elongation is hypothesized to be the primary cause of decreased plant growth in response to long‐term heavy grazing (LHG). However, it remains largely unknown how LHG‐induced changes in stem elongation are mediated by internode traits. Accordingly, we experimentally investigated the effects of LHG (defined as twice the stocking rate recommended by the local government) on plant stem elongation and internode allometry in Leymus chinensis in Xilinhot, Inner Mongolia, China. Plant size and internode traits, including internode length (IL), internode diameter (ID), and internode number (IN), from plant individuals were measured according to their phytomer position from base to apex. The results revealed that IN and their distributions were changed in response to LHG. Although LHG negatively affected IL and ID of each L. chinensis internode from base to apex and eventually stem length, the plasticity index of IL and ID increased initially and then decreased from the lowermost to the uppermost internode in response to LHG. These contrasting responses of internode traits were result of allometry between internode traits determined by both LHG and internode position. Ultimately, IL and IN were identified to be key traits influencing stem length reduction under LHG conditions and explaining 52.51% and 47.49% of variation in stem length, respectively. Overall, our findings suggest that the limitation of L. chinensis stem elongation induced by LHG is mediated by the plasticity and allometry of internode traits. This result emphasizes the sensitivity of individual plants to LHG and is potentially valuable for optimal grassland management.     

The potential for control of the soft rush (Juncus effusus) in grass pasture by grazing goats

Two experiments were conducted to examine the effect of inter-tussock grass height and stocking rate on the utilization of the rush ( Juncus effusus ) by grazing goats. In the first experiment, on rush-infested Festuca rubralTrifolium repens pasture, the utilization of rushes by goats grazing at a sward height of 3–4cm or 5–6cm was compared with that occurring on plots grazed by sheep at a sward height of 3–4 cm. Sheep grazed minimal amounts of rush. In contrast, it was estimated that 90% and 75% of current seasons growth of rush was grazed by goats at sward heights of 3–4 and 5–6 cm respectively during the first year. With continued goat grazing at 5–6cm there was a dramatic reduction in the cover and vigour of the rushes, and at a sward height of 3–4cm established tussocks were eliminated from the pasture.
The second experiment compared the utilization of rushes invading predominantly Agrostis swards stocked with goals at 10, 20 or 30 ha^-1 and in which inter-tussock sward height was maintained at 4–5cm on all treatments, by adding or subtracting sheep. On one site rush utilization increased with the increase in stocking rate of goats and rush tussocks were eliminated within 3 years at 30 goats ha^-1. On another, there was no difference between plots stocked at 20 or 30 goats ha^-1 and viable tussocks remained. The influence of the composition and productivity of the inter-tussock herbage and the proportion of rush in the biomass are discussed.
Goats can be used lo control rushes in grassland but high stocking levels and low inter-tussock pasture heights are required to promote adequate levels of utilization.     

Mixed‐grass prairie rhizome biomass is influenced by cattle grazing intensity

This study was conducted on a mixed‐grass prairie in south‐central North Dakota, USA, to test the effect of animal grazing on rhizome biomass. Below‐ground plant biomass samples were collected from pastures with moderate and heavy grazing by beef cattle. Because the biomass data did not meet the normality assumptions, the computer resampling method involving a nested anova was used. A reduction in rhizomes was found under heavy grazing, as compared with moderate grazing. Although rhizomes only accounted for a small fraction of total below‐ground plant biomass, our study suggested that the high rhizome density found in the moderately grazed pastures might be partly responsible for the greater potential of plant regrowth in the moderately grazed pastures than in the heavily grazed pastures on this mixed‐grass prairie.     

Seedling recruitment dynamics of forage and weed species under continuous and rotational sheep grazing in a temperate New Zealand pasture

Understanding the grazing conditions under which plant populations are limited by seed availability (seed limitation) is important for devising management schemes that aim to manipulate the establishment of weed and forage species. Seeds of three weed species (Cirsium arvense, C. vulgare and Rumex obtusifolius) and five forage species (Lolium perenne, Lotus uliginosus syn. L. pedunculatus, Paspalum dilatatum, Plantago lanceolata and Trifolium repens) were broadcast sown into L. perenne–T. repens pastures in Manawatu, New Zealand and five sheep‐grazing and two slug‐grazing (with and without molluscicide) treatments were imposed in a split‐plot design. Of the five sheep‐grazing treatments, four compared continuous grazing with rotational grazing at intervals of 12, 24 and 36 d in spring, with all four grazed under a common rotation for the remainder of the year. The fifth treatment was continuous grazing all year. Seed sowing increased seedling emergence of C. vulgare, L. perenne, P. lanceolata, R. obtusifolius and T. repens under all sheep‐ and slug‐grazing treatments, with differences in seedling densities persisting for at least 21 months. Seed sowing did not increase seedling densities of C. arvense, L. uliginosus or P. dilatatum. The effects of sheep‐grazing management on seedling emergence and survival were uncoupled. For the five seed‐limited species, seedling emergence was greater on pastures that were rotationally grazed during spring compared with those that were continuously grazed. However, seedling survival was lower in pastures grazed rotationally during summer, autumn and winter, so that after 21 months seedling numbers were greater on plots that were continuously grazed all year. Exclusion of slugs increased seedling recruitment of T. repens but had no impact on the other species. As weed and forage species responded in a similar way to sheep‐grazing management (increased under continuous, decreased under rotational), it is unlikely that the goals of reducing weed invasions and enhancing forage species establishment could be carried out concurrently in established pastures with the same management.     

Herbage intake and N excretion by sheep grazing monocultures or a mixture of grass and white clover

In 1988 and 1989, swards of grass (G0), while clover (C0) and grass/white clover (GC0) receiving no N fertilizer, and a grass sward supplied with 420 kg N ha^?1 (G420), were grazed by non-lactating sheep to maintain a sward surface height of 6 cm. Herbage organic matter (OM) intakes averaged between 1200 and 1700 g OM ewe^?1 d^?1. For treatments G0, C0, GC0 and G420 respectively, the ewes' live weight gain was 102, 112, 100 and 110 g d^?1 and changes in body condition scores were +0·28, +0·52, +0·36 and +0·44 units season^?1. However, the effect of treatment was not significant for either variable. There were similar levels of output of faecal N ewe^?1 but significantly more urinary N ewe^?1 was excreted on treatments C0 and G420, where the concentrations of N in herbage laminae were also higher. For example, in 1989, total daily N excreted was 39·7, 64·4, 44·0 and 63·3 g N ewe^?1 for G0, C0, GC0 and G420 respectively. Taking into account the mean daily stocking rates, which were 19·4, 26·6, 27·2 and 36·5 ewe ha^?1, the total faeces and urine returns over the season were 161, 358, 249 and 484 kg N ha^?1 for each treatment respectively. The herbage OM intakes ewes^?1 d^?1 measured in September and October were similar for C0 and G420, and so the intake of herbage OM ha^?1 d^?1 was related to stocking rate, i. e. the estimated herbage intake ha^?1 over the growing season for the white clover monoculture was 73% of that for N-fertilized grass. Excretal nitrogen returns to the pasture from grazed mono-cultures of clover were high, and similar to those from a grass sward receiving 420 kg fertilizer N ha^?1. Consequently potential losses of N to the environment are high under these management systems.     

Effect of structure of a tropical pasture on ingestive behaviour, digestibility of diet and daily intake by grazing cattle

The effect of the structure of a tropical pasture, based on Dichanthium spp., on the ingestive behaviour, in vivo digestibility of the diet and herbage intake by eight Creole tethered heifers was studied. Two levels of nitrogen fertilizer (0 and 50 kg ha^?1) were applied to plots after each grazing cycle and there were 28 d between each of the three grazing cycles. Four heifers grazed individual subplots daily on each plot for 14 d in each of the successive grazing cycles. Simultaneous measurements of bite depth, bite mass, biting rate, short‐term intake rate and daily grazing time were made in two 4‐d periods at the end of each 14‐d period. The in vivo organic matter digestibility (OMD) and daily herbage organic matter intake (OMI, expressed on a kg LW^0·75 basis) were also measured at the same times. Relationships among pasture characteristics and ingestive behaviour were similar to those reported in other short‐term studies: pasture height was highly correlated with bite depth, bite mass and biting rate (r = 0·91, r =0·79 and r = ?0·68, respectively, P < 0·001). Pasture variables had lower correlations with grazing time and short‐term intake rate than with bite depth, bite mass and biting rate. Pasture structure was more highly correlated with OMD than OMI: leaf mass and length and also the extended tiller length were highly correlated with OMD (r = 0·77, r = 0·76 and r = 0·72, respectively, P < 0·001) whereas the crude protein concentration of the herbage was correlated with OMI and digestible OMI (r = 0·50 and r = 0·69, respectively, P < 0·001). Ingestive behaviour variables, as well as OMD, were correlated more with pasture characteristics than was OMI.     

Effects of pre-treatment, renovation procedure and cultivar on the growth of white clover sown into a permanent pasture under both grazing and mowing regimes

White clover ( Trifolium repens ) is a valuable pasture component that is frequently present in insufficient quantity for optimal animal nutrition. Several methods of reintroducing white clover into a permanent pasture without conventional tillage were investigated. Three seeders (Hunter, Vredo and a conventional seed drill), two white clover cultivars (Sacramento, and Sonja), two pasture pre-treatments (a hard spring grazing or grazing plus light harrowing) and two defoliation regimes (grazing or mowing) were used to determine optimal seedling establishment conditions. Defoliation treatments were used as a method of investigating pasture improvement experiments. Measurements were taken to determine proportion of white clover present and total herbage mass.
Plots renovated using a Hunter drill had the highest white clover content in the months immediately after renovation. Subsequently pre-treatment method appeared to have no significant effect on herbage mass or species composition. The proportion of white clover in plots sown with the cultivar Sacramento was frequently higher than that in plots sown with the cultivar Sonja, but, overall, herbage production of cultivars was not different.
Mowed plots had higher herbage production and tended towards a greater white clover content than grazed plots. Compaction of the surface to a depth of 10 cm in the grazed plots may have been a factor in the observed difference in herbage production. Regardless of management, within two years white clover content was similar among all treatments, including controls.